Certain neurosurgical procedures require the determination of the precise location of target tissue, and fine discrimination of the target from adjacent non-target tissue. For example, during a "pallidotomy," a procedure often performed on patients with Parkinson's disease, the neurosurgeon must carefully introduce a lesioning device into a small area deep in the brain called the Globus pallidus internus (Gpi), while avoiding the adjacent Globus pallidus externus (Gpe). Computed tomography (CT) and magnetic resonance imaging (MRI) are typically used to guide the surgeon to the Gpi/Gpe region. More precise, localized targeting is often achieved by means of electrophysiological localization techniques.
Conventional electrophysiological localization techniques typically involve the insertion of a tungsten electrode into the brain to detect neural activity. Because different brain areas produce characteristic patterns of neural activity, the signals picked up by the electrode at different locations are used to finely distinguish between the different brain areas. The Gpe and Gpi, for example, produce different characteristic patterns of activity, as monitored on the tungsten electrode. This knowledge is used during a pallidotomy to determine the boundary between the two structures, which allows the subsequent introduction of a lesion into the Gpi while avoiding lesioning the Gpe.
Because the tungsten electrode detects activity at only one site in the brain at any given time, the surgeon moves the electrode sequentially to multiple sites, stopping at each site for some time to monitor the local neuronal activity. Typically the electrode is inserted into the brain at a few different surface locations, and several depth locations are monitored along each electrode insertion track. Characteristic patterns of neural activity are noted at several of these electrode locations. As this information builds up over the course of the surgery, the surgeon derives an anatomical and/or functional map of that part of the brain.
The success of electrophysiological localization depends largely on the skill of the surgeon, who must accurately position the electrode at several sites in the brain and then accurately interpret the measurements taken by the electrode. Even the slightest misguidance of the electrode or misinterpretation of the measurements can lead to brain damage. As the number of monitored sites increases, so does the time required, and therefore the risk of brain damage, the cost of surgery, and the risk to the patient's health.